risk factors for apical root resorption of maxillary ...€¦ · risk factors for apical root...

Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients

A. Davide Mirabella, DDS, MSD, = and Jon Artun, DDS, Dr. Odont. b Catania, Italy, and Seattle, Wash.

The purpose of this study was to identify risk factors for apical root resorption in adult orthodontic patients. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before and after treatment and treatment charts of 343 adults, representing groups of consecutively treated patients from four orthodontic practices, were examined. Apical root resorption was calculated by subtracting posttreatment tooth length measurements from the corresponding pretreatment measurements. Root width was measured from the mesial to the distal outline of the roots 4 mm from the apex. Root form was scored subjectively as normal, pointed, eroded, blunt, bent, and bottle shaped. Root movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Proximity of the central incisor roots to the palatal cortical bone was scored subjectively as present or absent. Severity of initial malocclusion and treatment variables were collected from the charts. Multiple linear regression analyses revealed that amount of root movement, long roots, narrow roots, abnormal root shape, and use of Class II elastics were significant risk factors. However, the statistical model had a low explained variance, strongly suggesting a weak prediction power. No association was found between type of initial malocclusion, treatment time, use of rectangular arch wires, proximity of the root to the palate or treatment with maxillary osteotomy, and root resorption. Endodontic treatment was a preventive factor. (AM J ORTHOD DENTOFAC ORTHOP 1995;108:48-55.)

S e v e r a l studies have documented that the averaged amount of apical root resorption is slight in a group of orthodontic patients. 1-8 The individual variation has been considerable, with only few patients affected severely. Such results suggest an individual predisposition and a multifac- torial cause, and may explain why results from studies of risk factors are equivocal. Simple corre- lations may be difficult to demonstrate, particularly in studies of small sample size.

Histologic studies reveal resorption lacunae on the pressure side of all teeth shortly after exposure to orthodontic forces. 9-11 Since force application causes tooth movement, an association may be expected between apical root resorption and movement of the root apex. Surprisingly few studies have analyzed this relationship directly. 1"~'12 Very small

This article is based on research submitted by the senior author in partial fulfillment of the requirements for the Master of Science in Dentistry degree, Department of Orthodontics, School of Dentistry, University of Washington. Supported by Washington Dental Service Foundation Grant no. 65-7973 and the University of Washington Alumni Association, aIn private practice, Catania, Italy. bprofessor, Department of Orthodontics, University of Washington, Seattle. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/52476

48

sample sizes may be one reason for negative findings. 7 More information is available on the effect of changes in tooth inclination, 1'7"13 overjet, 2'4'5"s and overbite 14 on root resorption. However, such changes do not necessarily reflect the amount of apical movement, which in part may explain why some studies have demonstrated significant relationships, 1'2'4'5'8 whereas others have not. 7 Similarly, length of treatment, time with rectangular arch wires, and time with different types of elastics may not correlate well with the time pressure is exerted on the roots. Accordingly, it may not be surprising that few studies have found any associationsY

Apical root form, short roots, and signs of previous root resorption are frequently mentioned risk factors for apical root resorption. However, few studies have evaluated those relationships, and the results are conflicting. 6'13'15"17

An increasing number of adults seek orthodontic treatment. Several have experienced orthodontic treatment during adolescence, resulting in blunting and shortening of the roots. The purpose of this study was to identify risk factors for apical root resorption in a large group of consecutively treated adult orthodontic patients, with special em- phasis on atypical root form, root length, amount of root movement, and type of treatment modality.

American Journal of Orthodontics and Dentofacial Orthopedics Mirabella and .~rtun 49 Volume 108, No. 1

N A B C D E

Fig. 1. Criteria for subjective scoring of root form as normal (IV), blunt (A), eroded (B), pointed (C), bent (19), bottle shaped (E).

MATERIAL AND METHODS Sample

Periapical radiographs of maxillary anterior teeth and cephalograms made before (T-l) and after (T-2) treatment and treatment charts of 500 adults, representing groups of consecutively treated patients from four orthodontic practices, were examined. Adult was defined as a minimum of 20 years of age at T-1. Multibonded appliances with 0.022 x 0.028-inch bracket slots were used in all cases. The radiographs were made in the same laboratory by using a paralleling long cone technique. Patients with incomplete records were omitted. A total of 343 patients, aged 20.0 to 70.1 years at T-1 (mean 34.5, SD 9.0) and treated for 0.6 to 5.2 years (mean 2.0, SD 0.7) were included in the study.

Examination of charts

Pretreatment malocclusion was recorded according to Angle's classification. A habit history was recorded as present if thumb sucking, tongue thrusting, nail biting, or parafunctional habits had lasted beyond 8 years of age. A history of traumatic injury was recorded as present if any trauma to the teeth or the face was reported. The severity of the trauma was not recorded. Treatment time was recorded as the time lapse between appliance place- ment and removal. Number of months with anterior vertical elastics, Class II elastics on either or both sides, and rectangular wires was recorded. Treatment with maxillary osteotomy was also recorded. History of earlier orthodontic treatment was recorded as present or absent. The recording was based on examination of the anam- nestle records and interview with the orthodontists.

Examination of periapical radiographs

After random coding for identification, the radiographs were projected onto a screen at about x 7 mag- nification. Tooth length (TL) was measured from the incisal edge to the root apex. Root width was measured from the mesial to the distal outline of the root 4 mm from the apex. The measurements were made with a transparent ruler to the nearest 0.14 mm, the nearest whole millimeter on the magnified image. The ruler was

placed along and perpendicular to the pulp canal, respectively. Root form was scored subjectively as normal, blunt, eroded, pointed, bent, or bottle shaped (Fig. 1). Presence of a root canal filling or an impacted canine was also recorded.

Examination of cephalograms

The outline and the trabecular pattern of the maxilla and the outlines of the pterygomaxillary fissure and the key ridges were traced on the cephalograms at T-1. The incisal edge (Is-l) and the long axis (ILs-1) of the maxillary incisor and the incisal edge (Ii-1) of the mandibular incisor were also traced. The cephalometric trac- ing at T-1 was superimposed on the corresponding cephalogram at T-2 according to the "best anatomic fit." The palatal plane (PP) was drawn as a line connecting the anterior and the posterior nasal spines. Then the incisal edge (Is-2) and the long axis (ILs-2) of the maxillary incisor at T-2 were traced. The angles ILs-1/PP ([3-1) and ILs-2/PP (13-2) were measured to the nearest 0.5 °. Overjet (O J) and the horizontal movement of the incisal edge during treatment (Dx) were measured par- allel to PP as the distances between Is-1 and Ii-1, and Is-1 and Is-2, respectively. Overbite (OB) and the vertical movement of the incisal edge during treatment (Dy), were measured perpendicular to PP as the distances between Is-1 and Ii-1, and Is-1 and Is-2, respectively. A transparent grid was used, and the measurements were made to the nearest 0.5 mm (Fig. 2). Proximity of the central incisor roots to the palatal cortical bone was scored subjectively as present or absent. The root was judged to be in close proximity to the palate if the lower third of the root was touching the cortical bone. The apex was judged to be in close proximity to the palate if an indentation was apparent in the outline of the cortical bone in the apical area (Fig. 3, A and B, respectively).

Error of the method

The reproducibility of the measurements was as- sessed by statistically analyzing the difference between double measurements taken at least 1 week apart on 40 series of periapical radiographs (21 at T-1 and 19 at T-2) and 40 cephalograms (20 at T-1 and 20 at T-2) selected

50 Mirabella and Artun American Journal of Orthodontics and Dentofacial Orthopedics July 1995

P.s ,Ns

\ ° , \ Fig. 2. Superimposition showing measurement of horizontal (Dx) and vertical (Dy) movement of incisal edge and change in tooth inclination from before (,8-1) to after (~-2) treatment relative to palatal plane. Horizontal (Dx') and vertical (Dy') movement of apex were calculated mathematically (see text).

cZ

A

Fig. 3. Criteria for subjective scoring of proximity of apical third of root to palatal cortical bone (A) and proximity of root apex to palate (B).

at random. The measurement error was calculated according to:

2

Sx= / ~

where D is the difference between duplicated measurements and N is the number of double measurements. 18 The mean error for the tooth length measurements was 0.34 mm with a range of 0.27 mm (right lateral incisor) to 0.42 mm (right canine). The errors were 0.34 mm for O J, 0.32 mm for OB, 0.40 mm for Dx, 0.61 mm for Dy, and 0.30 degree for [3.

Data analysis

Apical root resorption was calculated by subtracting TL at T-2 (TL-2) from TL at T-1 (TL-1). Sample means of amount of resorption of the most severely resorbed central and lateral incisor and canine per patient were calculated.

The horizontal (Dx') and vertical (Dy') movements of the apex of the maxillary central incisors from T-1 to T-2 were calculated according to the following formulas:

Dx' = Dx + (TL-1). [(cos [3-2) - (cos [3-1)] Dy' = Dy + (TL-1). [(sin [3-2) - (sin [3-1)]

A positive reading signified anterior movement or intrusion of the root apex. The absolute values for Dx' and Dy' were used in the statistical analyses. In addition, the values for Dy' were grouped in three categories: more than 0.5 mm intrusion, between 0.5 mm intrusion and 0.5 mm extrusion, and more than 0.5 mm extrusion. Multiple linear regression analyses were employed to test for any associations between apical root resorption and variables recorded from the charts and the radiographs (Table I). Separate analyses were made for central and lateral incisors and canines. The most severely resorbed tooth for each pair was used as the dependent variable. Two sets of runs were performed. Independent variables were eliminated in the second run if their effects were not significant at level 0.30 for any tooth.

The TL-1 for each pair of central and lateral incisors and canines was averaged into one value per pair. Mean TL-1 for central and lateral incisors and canines, mean Dx', and mean treatment time were calculated for the two subgroups of patients with and without a history of earlier orthodontic treatment. Student's t test for unpaired data was used to test for any statistically significant differences. A Chi Square test was used to test for any significant difference in frequency of teeth

American Journal of Orthodontics and Dentofacial Orthopedics Mirabella a n d / f r t u n 51 Volume 108, No. 1

with abnormal root shape at T-1 between the two subgroups.

RESULTS

Mean apical root resorption of the most severely resorbed central and lateral incisor and canine per patient was 1.47 mm (SD 1.40), 1.63 mm (SD 1.24), and 1.25 mm (SD 1.52), respectively.

The second run of regression analyses revealed that tooth length was associated with root resorption for all teeth, that history of earlier orthodontic treatment was a preventive factor for central and lateral incisors, and that endodontic treatment was a preventive factor for lateral incisors and canines. Horizontal movement of the apex was associated with root resorption for central incisors, apical root width was negatively associated for lateral incisors, and time of anterior elastics and Class II elastics wearing was associated with root resorption for canines. In addition, atypical root shape was a risk factor for root resorption for central incisors (Ta- ble II).

No differences in TL-1 were found between patients with and without a history of earlier orthodontic treatment (Table III), and no difference in mean Dx' was found between the two subgroups, 1.67 mm (SD 1.37) versus 1.55 mm (SD 1.40), respectively (P -- 0.66). Mean treatment time was shorter for patients with a history of earlier orthodontic treatment (19.2 months, SD 8.0) than for patients without (24.4 months, SD 8.9, P < 0.01). The frequency of teeth with abnormal root shape at T-1 was higher among patients with a history of earlier orthodontic treatment (31%) than among the patients without (18%, P < 0.05).

DISCUSSION

For years there have been suggestions that amount and type of tooth movement are major determinants for apical root resorption. 1'2's'19 How- ever, few previous studies have attempted to quan- tify the tooth movement. 1'7'12 In addition, the sample sizes have been small and previous methods have not reflected the amount of root movement. This may explain why one study failed to detect any association between tipping and bodily movement of the teeth and root resorption. 7 Our study is the first to perform an accurate evaluation of the relationship between movement of the root apex and apical root resorption in a large sample. Our sample of nongrowing patients facilitated superimposition of pretreatment and posttreatment cepha-

Table I . Variables used in the multiple linear regression model to test for any associations with apical root resorption

Independent variables Unit

Root width mm Root shape Normal/abnormal Tooth length (T-I) mm Endodontic treatment Yes/Not Overjet mm Overbite mm Trauma Yes/Not Age Months Habit Yes/Not Previous orthodontic treatment Yes/Not Angle class I; II, Division 1,2;

Il l Treatment time Months Treatment with rectangular AW Months Class II elastics Months Anterior vertical elastics Months LeFort I osteotomy Yes/Not Proximity to palate T-1 Yes/Not Proximity to palate T-2 Yes/Not Horizontal movement (Dx')* mm Vertical movement (Dy')* mm Direction of Dy'* 1/2/3 Presence of impacted canines** Yes/Not

*Applies to central incisors only. **Applies to lateral incisors only.

lograms. To avoid bias due to high method error associated with locating the root apex on the cephalograms, 2° we calculated apical movement from changes in position of the incisal edges and inclination of the teeth. The incisal edge and the long axis 'of the incisors can be identified with a high degree of accuracy, 2° as indicated in our method error study. For the same reason we used the measurements of tooth length on the periapical radiographs in the calculations. Tooth length before and after treatment was considered equal not to interpret root resorption as tooth movement. A high proportion of the patients in our sample underwent a change in incisor inclination during treatment. For that reason the pretreatment and posttreatment periapical films could not be placed in the exact same locations. However, bias due to variations in radiographic projections are likely to be small and randomly distributed in our material.

We could confirm our hypothesis that movement of the roots, either in an anterior or a posterior direction, is associated with apical root resorption. The amount of tooth movement in the vertical plane was small in our sample, with only

52 Mirabella and ~rtun American Journal of Orthodontics and Dentofacial Orthopedics July 1995

Table II. Results of the second run of l inear multiple regression analyses for the maxillary central incisors, lateral incisors, and canines

Independent variables Central incisors Lateral incisors Canines

Root width n.s. P < 0.05 n.s. Root shape P < 0.001 n.s. n.s. Tooth length (T-l) P < 0.0001 P < 0.0001 P < 0.0001 Endodontic treatment n.s. P < 0.05 P < 0.0001 Overjet n.s. n.s. n.s. Overbite n.s. n.s. n.s. Previous orthodontic treatment P < 0.05 P < 0.05 n.s. Treatment time n.s. n.s. n.s. Treatment with rectangular AW n.s. n.s. n.s. Class II elastics n.s. n.s. P < 0.05 Anterior vertical elastics n.s. n.s. P < 0.05 Proximity to palate T-1 n.s. - -- Horizontal movement (Dx') P < 0.05 - --

n.s. = Not significant.

Table Ill. Sample means (ram) of averaged tooth length for patients with (Or tho yes) and without (Or tho no) a history of earlier or thodont ic t rea tment for each pair of teeth per pat ient at T-1

Teeth N SD N SD

Central incisor 31 2.95 308 Lateral incisor 31 2.57 311 Canine 31 2.77 307

Ortho yes

Mean

23.66 22.51 26.27

OFtho no

Mean Significance

23.90 2.29 n.s. 22.99 2.04 n.s. 26.68 2.51 n.s.

11.5% of the patients showing more than 1 m m of intrusion and 25.4% more than 1 m m extrusion. Our finding that vertical tooth movemen t is not a risk factor should therefore be evaluated with care. There have been speculations that correct ion of open bites is a risk factor for root resorption. 5 The reason may be that tooth jiggling due to a high prevalence of tongue dysfunction in such cases increases the risk of resorp t ion? '14 Very few patients were recorded to have tongue dysfunction in our sample, and the validity of that chart recording may be quest ioned. Accordingly, our sample may not be considered suitable to test that hypothesis.

I t is controversial whe ther t r auma is a risk factor for apical root resorption. 4'5"21 o r n o t . a7

Malmgren et al. 17 found that the risk of resorpt ion in slightly or modera te ly t raumat ized teeth is not increased provided the or thodont ic t rea tment is s tar ted 4 to 5 months after t rauma, and no signs of inf lammatory resorpt ion could be observed. We did not have detai led informat ion on intensity, location, and type of t rauma, minimizing the impor tance of the negative findings in our sample.

Our regression model indicated that abnormal root shape is associated with apical root resorption, and agreed with previous studies. 6'13'I6"22 However, the relationship was significant only for central incisors, and we did not make any at tempts to differentiate be tween the various types of abnormal root anatomy. We also found an inverse relationship be tween apical root width of lateral incisors and root resorption. Al though we failed to demonstrate a significant relationship between both variables and root resorpt ion for the same pair of teeth, the findings may suggest that narrow roots with pointed or deviated apices are at high risk (Fig. 4). Simultaneous evaluation of p re t rea tment and pos t t rea tment radiographs of selected cases indicated that the resorpt ion process frequently was limited to the abnormal apical project ion (Fig. 5). A c o m m o n belief is that short roots un- dergo more root resorption. 6"13'16 However, our results support the opposi te opinion 15"22 and suggest that the tendency for resorpt ion increases with increasing tooth length. Possible explanations for this may be that longer tee th need stronger forces

American Journal of Orthodontics and Dentofacial Orthopedics Mirabella a n d A r t u n 53 Volume 108, No. 1

Fig. 4. Periapical radiographs made before (top) and after (bottom) orthodontic treatment of patient with long, narrow, and bent roots and excessive apical root resorption.

Fig. 5. Periapical radiographs made before (top) and after (bottom) orthodontic treatment of patient with resorption limited to abnormal apical projections.

to be moved, and that the actual displacement of the root apex is larger during tipping or torquing movements of longer teeth.

Our results confirm that endodontic treatment is a preventive factor for apical root resorption. This supports previous studies finding that endodontically treated teeth resorb significantly less than their contralateral controls 23'24 (Fig. 6). An- other author has reached different conclusionsY However, the majority of the teeth included in that study had been subjected to injury.

The regression model did not detect any association between alignment of impacted canines and apical root resorption Of the lateral incisors. How- ever, in our sample only 1.7% of the patients presented with impacted maxillary canines. A previous study found a significant relationship 5 and concluded that not only the eruption path, but also the force required for anchorage could explain the increased tendency for resorption.

A history of earlier orthodontic treatment was detected by the linear regression model as a pro- tective factor. This could not be explained by less amount of tooth movement in the patients seeking retreatment. The treatment time was shorter, but treatment time was not a risk factor in our study.

Fig. 6. Periapical radiographs made before (top) and after (bottom) orthodontic treatment of patient with and without endodontically treated central incisor. Note more apical root resorption of vital central incisor.

54 Mirabella and Artun American Journal of Orthodontk3 and Dentofacial Orthopedics July 1995

Fig. 7. Cephalograms and periapical radiographs made before (A and C) and after (B and D) orthodontic treatment of patient with proximity of root to palatal cortex. Note minor amount of apical root resorption.

One likely explanation for the finding may be that the orthodontists decided to limit the treatment objectives in a few patients judged to be at high risk due to evidence of resorption from the first treatment period. Another explanation may be that a high proportion of patients who have experienced severe root resorption elect not to seek retreatment. Accordingly, an overrepresentation of patients who are resistant to apical root resorption may have occurred in the subsample.

Proximity of the root apex to the palatal cortex has been associated with apical root resorp- t io i l , x6,a6,a7 Kaley and Phillips concluded that the risk of clinically significant apical root resorption increased 20 times when the maxillary incisors were in close proximity to the lingual or cortical plate£ 7 Our results are in agreement with an experimental study in monkeys, 2~ finding no increase in root resorption in such cases (Fig. 7). Our scoring showed that only in a few cases of maxillary incisor roots touching the cortical plate, did the apices actually contact the cortical bone. One explanation for the association found in previous studies 26'27 may be that teeth in close proximity to the palate posttreatment often experience a larger than aver- age root movement. Accordingly, the root resorption may be due to the amount of tooth movement rather than pressure from the cortical plate. Our findings also contradict Kaley and Phillips' conclu-

sion that LeFort I osteotomy is a risk factor for apical root resorption. 27 Previous studies have found periods of ischemia and hyperemia after LeFort I osteotomy, 29 which are likely reasons for observed pulpal changes long term? ° However, it is difficult to explain any association between LeFort I osteotomy and root resorption.

Our results confirmed our hypothesis that type of initial malocclusion may not be of importance for amount of apical root resorption during treatment. Several authors 2'4'5 believe that overjet is a powerful predictor for resorption. However, overjet can be corrected in several ways other than moving the roots of maxillary anterior teeth, such as growth adaptation in growing persons, anterior expansion of the mandibular dentition, and orthognathie surgery. Also, appliances may be present for longer periods without creating pressure on the teeth. In accordance with some previous investigations, 2'7'31 this may explain why treatment time was not detected as a predictor for resorption. Previous authors have suggested that type of mechanics, in particular the use of rectangular arch wires and Class II elastics for correction of overjet 4'5 are associated with root resorption. However, they did not analyze any difference in effect on different pairs of teeth. Our results indicate that the use of elastic forces may increase the risk of apical root resorption only on the tooth that support the elas-

American Journal of Orthodontics and Dentofacial Orthopedics Mirabella and Artun 55 Volume 108, No. I

tics, probably because of jiggling movements of the anchor teeth. Therefore it seems that biomechani- cally complex orthodontic treatment may lead to an increased risk for apical root resorption.

In conclusion, amount of root movement and presence of long, narrow, and deviated roots increase the risk for apical root resorption. In addition, use of elastics may be a risk factor for the teeth that support the elastics. However, our statistical model had a low explained variance, R 2 being 0.20, 0.16, and 0.21 for the central and lateral incisors and canines, respectively. Accordingly, a weak prediction power is strongly suggested. That finding indicates presence of etiologic or causative factors for apical root resorption that we were unable to disclose. Individual variation in biologic response to orthodontic forces may in part explain variation, and genetic predisposition s may be another important predisposing factor.

We thank Don Joondeph, DDS, MSD, Vince Kokich, DDS, MSD, Doug Ramsay, DDS, MSD, PhD, and Peter Shapiro, DDS, MSD for their support. We also thank Vince Kokich, DDS, MSD, Peter Shapiro, DDS, MSD, John Moore, DDS, MSD, and Gina Trask DDS, MSD, for providing the sample. Special thanks go to Mrs. Elisa Mirabella for her clerical assistance.

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Reprint requests to: Dr. Jon 2trtun Department of Orthodontics SM-46 University of Washington Seattle, WA 98195

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